The recovery of high purity lead oxide materials (99.99+%) from lead acid pastes has been a long standing requirement with the lead battery manufacturers. The lead has value only as a high purity material. Currently the commercial practice is to send this paste recovered from crushing lead batteries to the lead smelters who separately process this mix of red lead, lead sulfate with carbon to obtain a crude lead metal product. This lead metal is then separately reacted with flux and air to remove the contaminating impurities such as antimony, barium, calcium, sulfur, copper, arsenic and other metals.
Russian patent No. 2,398,758 to Pozhidaeva discloses a method of producing lead acetate by reacting lead metal and lead dioxide with acetic acid in the presence of an organic solvent and a stimulating iodine additive wherein lead dioxide is the reagent and oxidant with acetic acid to produce lead acetate.
In U.S. Pat. No. 4,222,769 spent battery paste is desulfurized and then transformed into metallic lead by roasting in the presence of a carbon reducing agent.
U.S. Pat. No. 4,769,116 discloses treating exhausted lead acid battery paste with sodium hydroxide to produce a solution of sodium sulfate and a desulfurized paste which is subjected to electro winning to produce metallic lead.
International Publication No. WO99/44942 discloses a process of producing lead monoxide from spent lead battery paste using fluxing agents and an organic reducing agent in a calcination step at a temperature of 400° C.-450° C.
U.S. Patent Publication No. 2010/043600 to Martini discloses a process for recovery high purity lead compounds from electrode paste slime. The process includes dissolving lead oxide in the paste in a suitable acid, reducing any insoluble lead dioxide with hydrogen peroxide, a sulfite or sulfurous anhydride, converting the lead oxide to lead sulfate and then treating the lead sulfate in a solution containing an acetate salt. The lead sulfate is then converted to a carbonate salt, oxide or hydroxide.
U.S. Patent Publication No. 2006/239903 discloses the production of lead hydrate or monoxide from residues containing lead in the form of sulfates, monoxides, etc. followed by the desulphurization of battery paste with a suitable carbonate or hydrate, calcinating the desulfurized material to get impure lead monoxide followed by leaching of the lead monoxide with acetic acid, followed by filtering and then treating with an alkaline hydroxide or alkaline earth hydroxide to obtain soluble acetates to get a precipitate of lead hydrate or lead monoxide.
U.S. Pat. No. 7,507,496 to Smith et al relates to the selective removal of sulfate from battery paste and recovering Pb3O4 which has small amounts of impurities and can be separated from the impurities by dissolution.
The prior art methods get high yields of lead oxide at the expense of purity or in the alternative high purity at the expense of yield.
It is therefore desirable to obtain both high yield and high purity when treating spent acid battery paste to obtain lead oxide.